He beheaded at least one slaver with a broadsword, or rather his men did.

Late in the evening, they called at the house of James P. Doyle and ordered him and his two adult sons, William and Drury, to go with them as prisoners. (Doyle's 16-year-old son, John, who was not a member of the pro-slavery Law and Order Party, was spared after his mother pleaded for his life.) The three men were escorted by their captors out into the darkness, where Owen Brown and his brother Frederick killed them with broadswords. John Brown Sr. did not participate in the stabbing but fired a shot into the head of the fallen James Doyle to ensure he was dead.

https://en.m.wikipedia.org/wiki/Pottawatomie_massacre